Ever wonder why kids’ test scores at some city charter schools are among the highest in the state — while two-thirds of traditional-school kids in the city are failing? Consider two news events.

First is what happened Monday: Nearly 25,000 kids at more than 75 charters in the city returned to school. That’s several days before next week’s start for traditional schools. (And some charters already have been open for more than a week.)

A charter school day is also typically longer. So all told, charter kids often get the equivalent of a month or so more class time than regular kids over the course of a year.

We’re not saying this is the reason they do better (though it might help explain it). After all, if schools are lousy, what’s the point of longer hours? But the added face time at charters says a lot about attitudes at these schools compared to regular schools.

As does the other piece of news: As The Post reported, the United Federation of Teachers (which primarily represents traditional-school staff) is suing to make sure principals can’t interfere with teachers’ lesson plans.

Yet with so many of their kids failing, more — not less — oversight seems warranted.

UFT boss Mike Mulgrew argues that teachers should decide what happens in the classroom. Maybe so — if they were also willing to pay the consequences for poor results. Instead, the union has fought even merely having teachers evaluated, let alone fired for poor performance.

Other factors, of course, likely contribute to better charter scores, and in fairness, not all charters do well. But it’s pretty clear which approach to education many city moms and dads prefer: More than 50,000 kids are on waiting lists for charter seats.